1. Field of the Invention
The present invention relates to a linear motion rolling guide unit which is applied to sliding portions of machine tools, processing equipment, and testing equipment, and in which sliders slide on track rails with a number of rolling elements interposed therebetween.
2. Description of the Prior Art
In a conventional linear motion rolling guide unit, when a slider slides on a track rail, the seal between the slider and the track rail is provided by end seals mounted at both ends of the slider and an under seal mounted to the underside of the slider.
A conventional linear motion rolling guide unit as shown in FIG. 9 has been disclosed. As shown in the figure, the linear motion rolling guide unit consists mainly of a track rail 1 with raceway grooves 9 formed longitudinally extending on both side walls 11 thereof and a slider 20 slidably mounted astride the track rail 1. The slider 20 includes a casing 2, which is slidable relative to the track rail 1 and has raceway grooves 8 formed at positions facing the raceway grooves 9, a number of rolling elements or balls 4, which are trapped between the opposing raceway grooves 8, 9 to allow relative motion between the rail and the casing, and end caps 5 attached to the longitudinal ends of the casing 2.
The end cap 5 is fitted with an end seal 19 that provides a seal between the track rail 1 and the slider 20. The casing 2 is provided with an under seal 3 to seal the casing 2, the longitudinal side walls 11 of the track rail 1 and the underside of the casing 2.
The slider 20 is mounted astride the track rail 1 and is freely slidable on the rail 1 because of the presence of a number of balls 4 that circulate along the raceway grooves 9 in the rail 1. The balls 4 roll in a raceway 24 formed between the raceway groove 9 in the track rail 1 and the raceway groove 8 in the casing 2 and are led into a direction changing passage (indicated by 23 in FIG. 3) formed in the end cap 5 and further into a return passage 22 formed parallel to the raceway groove 8 in the casing 2, so that the balls 4 roll to circulate in an endless raceway.
The under seal 3 is simple in shape and thus can be manufactured easily. However, the under seal 3 has the drawback of being easily deformed by positioning errors of the casing 2 and the track rail 1 forming raceway grooves 8, 9 therein and by external force because it is formed of a thin plate. To describe in more detail, when the slider 20 slides on the track rail 1, any temperature variations and swelling by lubricant of the under seal 3 will deform the under seal 3 itself degrading its sealing performance.
Further, in the linear motion rolling guide unit the under seal 3 is secured at both ends to the casing 2 made of a metal by screws, so that when the under seal 3 formed of plastic such as synthetic resin soaks up lubricant and swells after a long period of service, it cannot move relative to the casing 2 and thus will deform. Once the under seal 3 deforms, the tight sealing or contact between the underside of the casing 2 and the upper surface of the under seal 3 fails, or the sealing portion deforms. In the linear motion rolling guide unit, when the sealing contact between the sealing portion and the side surfaces 11 of the track rail 1 degrades, the sealing performance, particularly the dust sealing effect, deteriorates.
Among the dust sealing apparatuses used in the linear motion rolling guide unit are those disclosed by Japanese Utility Model Laid-Open No. 118317/1991, 121220/1991, 19918/1992, 23818/1992 and 25028/1992.
The under seal device for the linear guide bearing disclosed in the Japanese Utility Model Laid-Open No. 118317/1991 has projections formed at the axial ends of the under seal that extend in the axial direction to fit into engagement openings formed in the bottom surfaces of the side seals. The under seal is easily attached to or detached from the side seals of large strength so as to increase the strength of the under seal.
The under seal device for the linear guide bearing disclosed in the Japanese Utility Model Laid-Open No. 121220/1991 has a two-pronged projection, at both axial ends of the under seal, projecting toward the bottom surface of the slider whose prongs can open in an inverted V-shape and be resiliently deformed toward each other. The bottom surface of the slider is formed at each axial end with a vertical hole, in which the two-pronged projection of the under seal fits, and with a through-hole that pierces through the sleeve portion of the slider in a direction perpendicular to the vertical hole so that one of the prongs engaged in the vertical hole elastically deforms to urge the under seal toward the side surface of the guide rail, bringing the side edge of the under seal into sliding contact with the guide rail.
Further, in the dust sealing apparatus for the linear guide apparatus disclosed in the Japanese Utility Model Laid-Open No. 19918/1992, the end of the under seal, which closes an opening in the lower part of a gap between the slider and the guide rail, is inserted between the bent surface of the side seal and the underside of the end cap to allow one-action removal and mounting of the under seal. The under seal is formed as a rectangular strip almost equal in length to the slider and the end of the under seal is fitted between the bent surface of the side seal and the underside of the end cap.
In the dust sealing device for the linear guide apparatus of the Japanese Utility Model Laid-Open No. 23818/1992, the side seal that seals openings at the front and back of a gap between the slider and the guide rail is inserted into a recessed groove formed at the end of the opening in the end cap.
The dust sealing device for the linear guide apparatus disclosed by the Japanese Utility Model Laid-Open No. 25018/1992 presses the side seal and the under seal against the sealing surface under a predetermined pressure by spring elasticity instead of the rubber elasticity to prevent early degradation of sealing function caused by the rubber abrasion, absorb greater effects of dimensional errors and enable stable, easy mounting and dismounting of the side seal and under seal.
The under seal devices for the linear guide bearings or the dust sealing devices for the linear guide apparatuses disclosed in the above publications, like the previously mentioned, conventional linear motion rolling guide unit, do not have the construction that permits deformation of the under seal in the axial direction and therefore have the similar problems. That is, the dust sealing member and the end cap are generally formed of different materials so that their thermal expansions caused by temperature variations differ from each other. When the thermal expansion of the dust sealing member becomes larger than that of the end cap, the dust sealing member deflects producing a gap between it and the rail or the underside of the sleeve, degrading the sealing effect and making it impossible to prevent dust from entering the raceway.